It is known to mount solid state light sources, such as semiconductor light emitting devices, in packages that may provide protection, color selection, focusing, and the like, for light emitted by the light emitting device. A solid state light emitting device may be, for example, an organic or inorganic light emitting diode (“LED”). Some packages for light emitting diodes are described in U.S. Pre-grant Publication Nos. 2004/0079957, 2004/0126913, and 2005/0269587 which are assigned to the assignee of the present invention, and which are incorporated herein by reference as if set forth fully herein.
Packages as described in the above referenced publications may be suitable for high power, solid state illumination applications. However, notwithstanding the advances described therein, there remains a need for improved packages in which multiple LEDs may be mounted. In particular, in some general lighting applications it may be desirable for an LED package to include multiple LEDs emitting in different regions of the visible spectrum. Light emitted by the LEDs may combine to produce a desired intensity and/or color of light, such as white light or any other desired color. In that case, it may be desirable for the LEDs in the package to be mounted relatively closely together.
A typical leadframe-based LED package includes electrical leads, contacts or traces for electrically connecting the LED package to an external circuit. In a typical LED package 10 illustrated in FIG. 1A, an LED chip 12 is mounted on a reflective cup 13 by means of a solder bond or conductive epoxy. One or more wirebonds 11 connect the ohmic contacts of the LED chip 12 to leads 15A and/or 15B, which may be attached to or integral with the reflective cup 13. The reflective cup 13 may be filled with an encapsulant material 16 containing a wavelength conversion material such as a phosphor. Light emitted by the LED at a first wavelength may be absorbed by the phosphor, which may responsively emit light at a second wavelength. The entire assembly is then encapsulated in a clear protective resin 14, which may be molded in the shape of a lens to collimate the light emitted from the LED chip 12. However, heat retention may be an issue for a package such as the package 10 shown in FIG. 1A, since it may be difficult to extract heat through the leads 15A, 15B, as both leads 15A, 15B cannot be connected to a heatsink, or they will be electrically shorted. Furthermore, both leads 15A, 15B are usually made of thin sheet metal of 0.50 mm maximal thickness, beyond which it is difficult to be manufactured and handled.
A conventional surface-mountable leadframe-based package 20 is illustrated in FIG. 1B. The package 20 includes an LED chip 22 mounted on a reflective cup 23. One or more wirebonds 21 connect the ohmic contacts of the LED chip 22 to leads 25A and/or 25B, which may be attached to or integral with the reflective cup 23. A clear protective resin 24 is cast around the assembly. The reflective cup 23 may be formed by stamping a thin sheet of metal when the leadframe is formed. Stamping the reflective cup 23 may result in thinning of the base and/or sidewalls of the cup 23, thus reducing its thermal spreading properties and capacity to dissipate heat generated by the semiconductor chips mounted at the bottom of the cup. Hence, less heat is extracted out of the package through the leads 25A, 25B, resulting in higher thermal resistance that limits the performance of the device. This type of package usually can handle a maximum power up to only about 0.5 Watt.